Isolation and characterization of T cells receptors for antigens is of great importance because little is known about the molecular underpinnings of the recognition systems on the cell surface of thymus derived lymphocytes. We have chosen to study the receptors for human histocompatibility antigens (HLA-A and B) on cytotoxic T lymphocytes, because of: 1) the paramount importance of the products of the major histocompatibility complex in cellular immunology, 2) accessibility to biochemical studies of the process of T cell killing, and 3) the availability of large quantities of well characterized human histocompatibility antigens. The intention of the proposed studies is to apply techniques developed in cell surface receptor research such as radioreceptor assay, photoaffinity labelling and affinitychromatography to describe properties of the T cell receptor for HLA antigens. Experiments are designed to study the heterogeneity and complexity of these receptors in allogeneic and syngeneic systems. In the latter case vesicular stomatitis virus infected lymphoblastoid cell lines will be used as stimulator and target cells in an in vitro cell mediated cytotoxicity system. In addition we will try to raise a heteroantiserum against HLA receptors on cytotoxic T cells to be used both in delineating the receptor properties and screening for large source of material. It is expected that these studies will not only be of theoretical but also of clinical importance in transplantation and autoimmune diseases.